Millimeter-wave frequencies generally refer to signals in the frequency band between approximately 30 GHz to 300 GHz, which are frequently used in various applications such as wireless personal area networks (WPANs), automobile radar, and image sensing. FIG. 1A illustrates a block diagram of one example of a millimeter wave receiver 100 including a low noise amplifier (LNA) 102, a mixer circuit 104, and a frequency synthesizer 106. Frequency synthesizer 106 includes a voltage controlled oscillator (VCO) 108, a divider circuit 110, a phase frequency detector (PFD) 112, a charge pump (CP) 114, and a low pass filter (LPF) 116.
As illustrated in FIG. 1A, the first active component of a millimeter wave receiver 100 is the LNA 102. Various LNAs for millimeter waves have been disclosed. For example, millimeter-wave LNAs were initially implemented in Group III-V compound semiconductors or implemented using cascode amplifiers based on binary junction transistor (BJT) technology. However, LNAs implemented using compound III-V semiconductors or BJTs are not easily integrated with the other components of the receiver, especially for digital circuits, resulting in higher implementation costs.
Recent advances in complementary metal oxide semiconductor (CMOS) technologies have enabled millimeter-wave integrated circuits to be implemented at lower costs as multi-stage LNAs. However, these multi-stage LNAs experience passive losses across the input, inter-stage, and output matching networks, which lead to insufficient gain. Consequently, the amplitude of the amplified signal after the LNA is too small to be accurately processed by the rest of the circuitry of receiver 100 illustrated in FIG. 1A.
Variable gain LNAs select the appropriate gain based on the distance between the transmitter and receiver. For example, when a transmitting antenna 120 is located at a distance D1 that is far away from a receiving antenna 118 as illustrated in FIG. 1B, the high gain mode of operation for the LNA 102 is selected. Conversely, when the receiving antenna 118 is positioned at a distance D2 that is close to the transmitting antenna 120 as shown in FIG. 1C, the low-gain mode of operation for the LNA 102 is selected.
However, the gain of the CMOS millimeter-wave variable gain LNAs are restricted due to the high-frequency operation. For example, the cascade of cascode gain stages to boost the gain results in an increase in passive losses and the inability to efficiently boost the gain when the direct current (DC) power increases. Additionally, these variable gain LNAs have a small dynamic range and thus the components of the LNAs must be carefully selected for specific applications.